The trypanosomatids Trypanosoma cruzi and the T. brucei group cause Chagas' disease and African sleeping sickness, respectively. Little effort is being placed on identifying new targets for developing a rational therapy against these diseases. The applicant has found that several strains of Trypanosoma contain an enzyme not present in mammals (NADH-fumarate reductase) which produces succinate, and allows a section of the Krebs' cycle to operate in reverse. In many trypanosomatids, succinate has a dual role, as a metabolic end product secreted to the extracellular environment and as an important respiratory substrate for cells with a complete respiratory chain (epimastigotes or procyclic trypomastigotes). The applicant believes succinate has a central role in intermediate metabolism of T. brucei, and intends to characterize the metabolic role of fumarate reductase as a succinate-producing enzyme. This enzyme is also present in bloodstream forms (in which the respiratory chain is not active), but its physiological role in these forms is unknown. Fumarate reductase was initially thought to be associated to the membrane fraction. The applicant has found, however, that this enzyme may be solubilized at high ionic strength, a first step towards its purification. The applicant proposes to: 1) purify and study this enzyme from T. brucei trypomastigotes and from procyclic trypomastigotes; 2) characterize four available inhibitors of the purified enzyme; 3) determine the metabolic function of this enzyme in the intermediate metabolism of T. brucei procyclic trypomastigotes by monitoring substrate accumulation, succinate production and NAD(P)H oxidation with glucose and proline as substrates, and 4) investigate its intracellular localization.